Positive Measurement

These two fundamental modes of measurement, collapse/positive measurement and interaction-free measurement are inherent in the measurement postulate.

Collapse/Positive Measurement

Let us examine what collapse, which occurs in positive measurement, appears as in the graphical simulation below:

Here there is a ball that is approaching a ring which represents the detector.  The ball is representative of a unitary wave function.  Note that the detector initially does not move or change its position when interacting with the wave-function.  Once the presence of the ball is detected, one should note two important features that occur.  Firstly, the wave function ceases to exist; it has been absorbed by the detector indicative of a positive measurement.  Secondly, the detector changes its state due to the momentum it has received from the absorption of the quantum of energy that has been measured. This causes the detector to tumble backwards in the graphical simulation.